Russian Defense Minister Sergei Shoigu held several calls with his American and European counterparts over the weekend following months of relative silence between Moscow and the West.

The main topic of the conversations was the conflict in Ukraine, with a focus on avoiding red lines that could lead to escalation, according to readouts from each interlocutor. In many of the calls, Shoigu claimed that Kyiv is planning to use a “dirty bomb,” or an explosive device that spreads nuclear material upon detonation but is not a full nuclear weapon. 

Western leaders flatly rejected the accusation, implying that Moscow is using it to set the stage for a “false flag” attack that the Kremlin can blame on Kyiv. “The world would see through any attempt to use this allegation as a pretext for escalation,” the U.S., Britain, and France wrote in a joint statement following the calls. The Kremlin has not publicly shared any information to back up its allegation.

Meanwhile, Russian media reported that, in a rare move, Moscow is deploying its military team that specializes in containing nuclear, chemical, or biological contamination.

George Beebe, the director of grand strategy at the Quincy Institute, said the reports are a stark reminder that the war “could rapidly escalate into a direct U.S.-Russian confrontation.” The calls also give a glimpse into internal Russian debates about the conflict, according to Beebe.

“Debate inside Russia has concluded that the West has lost its fear of nuclear war, and that as a result Russia needs to reestablish the ‘balance of terror’ that it believes underpinned stability during the Cold War,” he said.

“It is unclear to what degree these reports reflect a Russian effort to restore that Western fear of nuclear war, and to what degree if any Moscow actually suspects some Ukrainian groups might be preparing to use a radiological weapon,” Beebe added. “Either explanation is fraught with danger of escalation.”

Despite the joint response from Western leaders, there is some evidence of differences within the bloc. Paris was the only government to say it would refuse to be drawn into an escalation spiral, adding that it favors a peaceful resolution to the conflict. And NATO ally Turkey did not add its voice to the joint statement despite also having held a call with Shoigu over the weekend.